Add pattern to parent-children style file layout.

## Currently style

There are all languages folders on same layer.

```
- index.html
- en/
  - (English contens)
- ja/
  - (Japanese contens)
```

## Adding style

1. Put contents of default language on root of builder.
2. Put contents of other supportede languages on sub directory.

```
- (English contens)
- ja/
  - (Japanese contens)
```
